Adaptive voice frequency repeaters which employ echo cancelers to maximize return loss, or, stated another way, to minimize reflected signals, tend to be susceptible to "low" frequency signals. The echo cancelers have a limited number of taps, i.e., amplitude coefficients, to synthesize an impulse response characteristic of an echo path. Problems arise when excessive low frequency energy is in the input to the cancelers because of the limited number of taps. That is, a number of the taps are needed to deal with the low frequency signals and, then, there is an insufficient number of taps to synthesize a proper impulse response for the voice frequency band echo path.
One way to correct these problems is simply to increase the number of taps in the echo canceler. This solution, however, is inacceptable in most applications because of the need for additional memory, processing real estate on a chip and the like. All of which increase the cost of the echo canceler.